Re: [PATCH] Add linux-next specific files for 20220923

From: syzbot
Date: Sat Sep 24 2022 - 11:55:37 EST

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> Hi,
>
> On Sat, 24 Sept 2022 at 19:44, Hawkins Jiawei <yin31149@xxxxxxxxx> wrote:
>>
>> Hi Kees,
>> On Sat, 24 Sept 2022 at 15:26, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> >
>> > On Sat, Sep 24, 2022 at 03:10:34PM +0800, Hawkins Jiawei wrote:
>> > > From: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
>> > >
>> > > > Hello,
>> > > >
>> > > > syzbot found the following issue on:
>> > > >
>> > > > HEAD commit: 483fed3b5dc8 Add linux-next specific files for 20220921
>> > > > git tree: linux-next
>> > > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1154ddd5080000
>> > > > kernel config: https://syzkaller.appspot.com/x/.config?x=849cb9f70f15b1ba
>> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=473754e5af963cf014cf
>> > > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>> > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=157c196f080000
>> > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11f12618880000
>> > > >
>> > > > Downloadable assets:
>> > > > disk image: https://storage.googleapis.com/syzbot-assets/1cb3f4618323/disk-483fed3b.raw.xz
>> > > > vmlinux: https://storage.googleapis.com/syzbot-assets/cc02cb30b495/vmlinux-483fed3b.xz
>> > > >
>> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> > > > Reported-by: syzbot+473754e5af963cf014cf@xxxxxxxxxxxxxxxxxxxxxxxxx
>> > > >
>> > > > ------------[ cut here ]------------
>> > > > memcpy: detected field-spanning write (size 8) of single field "&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
>> > > > WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623 wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
>> > > > Modules linked in:
>> > > > CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted 6.0.0-rc6-next-20220921-syzkaller #0
>> > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2022
>> > > > RIP: 0010:wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
>> > > > Code: fa ff ff e8 cd b9 db f8 b9 04 00 00 00 4c 89 e6 48 c7 c2 e0 56 11 8b 48 c7 c7 20 56 11 8b c6 05 94 8e 2a 05 01 e8 b8 b0 a6 00 <0f> 0b e9 9b fa ff ff e8 6f ef 27 f9 e9 a6 fd ff ff e8 c5 ef 27 f9
>> > > > RSP: 0018:ffffc90003b2fbc0 EFLAGS: 00010286
>> > > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
>> > > > RDX: ffff888021d157c0 RSI: ffffffff81620348 RDI: fffff52000765f6a
>> > > > RBP: ffff88801e15c780 R08: 0000000000000005 R09: 0000000000000000
>> > > > R10: 0000000080000000 R11: 20676e696e6e6170 R12: 0000000000000008
>> > > > R13: ffff888025a72640 R14: ffff8880225d402c R15: ffff8880225d4034
>> > > > FS: 0000555556bd9300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
>> > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> > > > CR2: 00007fbda677dfb8 CR3: 000000007b976000 CR4: 00000000003506e0
>> > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> > > > Call Trace:
>> > > > <TASK>
>> > > > ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
>> > > > wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
>> > > > wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
>> > > > wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
>> > > > wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
>> > > > sock_ioctl+0x285/0x640 net/socket.c:1220
>> > > > vfs_ioctl fs/ioctl.c:51 [inline]
>> > > > __do_sys_ioctl fs/ioctl.c:870 [inline]
>> > > > __se_sys_ioctl fs/ioctl.c:856 [inline]
>> > > > __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
>> > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> > > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>> > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd
>> > > > RIP: 0033:0x7fbda6736af9
>> > > > Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
>> > > > RSP: 002b:00007ffd45e80138 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> > > > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fbda6736af9
>> > > > RDX: 0000000020000000 RSI: 0000000000008b04 RDI: 0000000000000003
>> > > > RBP: 00007fbda66faca0 R08: 0000000000000000 R09: 0000000000000000
>> > > > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fbda66fad30
>> > > > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>> > > > </TASK>
>> > >
>> > > I think this is the samiliar problem as what Kees Cook pointed out in
>> > > https://lore.kernel.org/linux-next/202209211250.3049C29@keescook/
>> > >
>> > > It seems that memcpy() will performs run-time buffer bounds
>> > > checking, which triggers this warning.
>> > >
>> > > #syz test git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>> > > master
>> > >
>> > >
>> > > diff --git a/include/linux/wireless.h b/include/linux/wireless.h
>> > > index 2d1b54556eff..81603848b0aa 100644
>> > > --- a/include/linux/wireless.h
>> > > +++ b/include/linux/wireless.h
>> > > @@ -26,7 +26,10 @@ struct compat_iw_point {
>> > > struct __compat_iw_event {
>> > > __u16 len; /* Real length of this stuff */
>> > > __u16 cmd; /* Wireless IOCTL */
>> > > - compat_caddr_t pointer;
>> > > + union {
>> > > + compat_caddr_t pointer;
>> > > + __DECLARE_FLEX_ARRAY(__u8, pointer_flex);
>> > > + };
>> >
>> > Is this expected to be dynamically sized? I assume so, given the "Real
>> > length" comment. :)
>> I think this is dynamically sized.
>>
>> hdr_len = compat_event_type_size[descr->header_type];
>> event_len = hdr_len + extra_len;
>>
>> [...]
>>
>> /* Add the wireless events in the netlink packet */
>> nla = nla_reserve(compskb, IFLA_WIRELESS, event_len);
>> if (!nla) {
>> kfree_skb(skb);
>> kfree_skb(compskb);
>> return;
>> }
>> compat_event = nla_data(nla);
>>
>> [...]
>>
>> if (descr->header_type == IW_HEADER_TYPE_POINT) {
>> compat_wrqu.length = wrqu->data.length;
>> compat_wrqu.flags = wrqu->data.flags;
>> memcpy(&compat_event->pointer,
>> ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
>> hdr_len - IW_EV_COMPAT_LCP_LEN);
>> if (extra_len)
>> memcpy(((char *) compat_event) + hdr_len,
>> extra, extra_len);
>> } else {
>> /* extra_len must be zero, so no if (extra) needed */
>> memcpy(&compat_event->pointer, wrqu,
>> hdr_len - IW_EV_COMPAT_LCP_LEN);
>> }
>>
>> according to the above code, it seems that this structure is used to
>> parse ths payload from buffer, so the field **pointer** should just
>> be a position label to the unused bytes in buffer. Its unused bytes will be
>> parsed as different structure according to event type.
>>
>> >
>> > > };
>> > > #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
>> > > #define IW_EV_COMPAT_POINT_OFF offsetof(struct compat_iw_point, length)
>> > > diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
>> > > index 76a80a41615b..9d0b50abbe09 100644
>> > > --- a/net/wireless/wext-core.c
>> > > +++ b/net/wireless/wext-core.c
>> > > @@ -620,7 +620,7 @@ void wireless_send_event(struct net_device * dev,
>> >
>> > adding in more context code:
>> >
>> > memcpy(&compat_event->pointer,
>> > ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
>> > hdr_len - IW_EV_COMPAT_LCP_LEN);
>> > if (extra_len)
>> > memcpy(((char *) compat_event) + hdr_len,
>> > extra, extra_len);
>> >
>> > The code above has "pointer" as a memcpy destination as well. I think
>> > that should be changed to pointer_flex as well, as the length calculation
>> > is the same. I wonder what FORTIFY will think about the second memcpy
>> > above. If I'm reading the math correctly, it might need to be:
>> >
>> > if (extra_len) {
>> > size_t offset = hdr_len - offsetof(typeof(*compat_event), pointer_flex);
>> > memcpy(&compat_event->pointer_flex[offset], extra, extra_len);
>> > }
>> >
>> I agree with you. It seems that in this situation,
>> the event type has been cleared, the unuesd bytes start from **pointer**
>> field should be parsed as struct iw_point type as below, which is a bigger
>> structure than **pointer**, it will also triggers the memcpy() warning.
>> /*
>> * The problem for 64/32 bit.
>> *
>> * On 64-bit, a regular event is laid out as follows:
>> * An iw_point event is laid out like this instead:
>> * | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
>> * | event.len | event.cmd | p a d d i n g |
>> * | iwpnt.len | iwpnt.flg | p a d d i n g |
>> * | extra data ...
>> *
>> * The second padding exists because struct iw_point is extended,
>> * but this depends on the platform...
>> *
>> * On 32-bit, all the padding shouldn't be there.
>> */
>>
>> And as for the value of offsetof in calculating **offset**,
>> I wonder if we can use the macro defined in
>> include/linux/wireless.h as below, which makes code simplier:
>> #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
>>
>>
>> >
>> > > } else {
>> > > /* extra_len must be zero, so no if (extra) needed */
>> > > - memcpy(&compat_event->pointer, wrqu,
>> > > + memcpy(&compat_event->pointer_flex, wrqu,
>> > > hdr_len - IW_EV_COMPAT_LCP_LEN);
>> > > }
>> > >
>> >
>> > But otherwise, yes, looks like the right modification. Thanks for tackling
>> > this! It is quite a weird structure! :)
>> >
>> > -Kees
>> >
>> > --
>> > Kees Cook
>
> hdr_len = compat_event_type_size[descr->header_type];
> event_len = hdr_len + extra_len;
>
> [...]
>
> /* Add the wireless events in the netlink packet */
> nla = nla_reserve(compskb, IFLA_WIRELESS, event_len);
> if (!nla) {
> kfree_skb(skb);
> kfree_skb(compskb);
> return;
> }
> compat_event = nla_data(nla);
>
> if (descr->header_type == IW_HEADER_TYPE_POINT) {
> [...]
> memcpy(&compat_event->pointer,
> ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> hdr_len - IW_EV_COMPAT_LCP_LEN);
> if (extra_len)
> memcpy(((char *) compat_event) + hdr_len,
> extra, extra_len);
> } else {
> /* extra_len must be zero, so no if (extra) needed */
> memcpy(&compat_event->pointer, wrqu,
> hdr_len - IW_EV_COMPAT_LCP_LEN);
> }
>
>
> According to above code, it seems that kernel will saves enough memory
> (hdr_len + extra_len bytes) for payload structure in
> nla_reserve()(Please correct me if I am wrong), pointed by compat_event.
> So I wonder if we can use unsafe_memcpy(), to avoid unnecessary
> memory() check as below, which seems more simple:
>
> #syz test git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

want 2 args (repo, branch), got 5

>
> diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> index 76a80a41615b..a967da647e2b 100644
> --- a/net/wireless/wext-core.c
> +++ b/net/wireless/wext-core.c
> @@ -609,19 +609,26 @@ void wireless_send_event(struct net_device * dev,
>
> compat_event->len = event_len;
> compat_event->cmd = cmd;
> +
> + /* kernel reserves event_len's bytes for compat_event,
> + * so we don't need memcpy()'s bounds check
> + */
> if (descr->header_type == IW_HEADER_TYPE_POINT) {
> compat_wrqu.length = wrqu->data.length;
> compat_wrqu.flags = wrqu->data.flags;
> - memcpy(&compat_event->pointer,
> + unsafe_memcpy(&compat_event->pointer,
> ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> - hdr_len - IW_EV_COMPAT_LCP_LEN);
> + hdr_len - IW_EV_COMPAT_LCP_LEN,
> + /* compat_event has enough room */);
> if (extra_len)
> - memcpy(((char *) compat_event) + hdr_len,
> - extra, extra_len);
> + unsafe_memcpy(((char *) compat_event) + hdr_len,
> + extra, extra_len,
> + /* compat_event has enough room */);
> } else {
> /* extra_len must be zero, so no if (extra) needed */
> - memcpy(&compat_event->pointer, wrqu,
> - hdr_len - IW_EV_COMPAT_LCP_LEN);
> + unsafe_memcpy(&compat_event->pointer, wrqu,
> + hdr_len - IW_EV_COMPAT_LCP_LEN,
> + /* compat_event has enough room */);
> }
>
> nlmsg_end(compskb, nlh);

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